Was Cash on Delivery introduced by Flipkart before Amazon in India? If so, I think amazon is 'imitating' flipkart in this area. I see COD on UPS, Fedex in USA but not as popular as COD in India.
eBay.in offered cash on delivery waaay before flipkart (as a matter of fact, the original site Baazee.com which got merged into eBay did it very successfully too)
The form of COD in India has been around for over a century across nearly the entire industrialized world. There's nothing innovative about it, the debate (Flipkart vs Amazon) is pretty moot given the history of COD stretches so far back.